XX (hair pin)

XXI (dog leg)

XXII (staircase, cat)

XXIII (exit)

Yellowline

Wikipedia:

Ariadne's thread, named for the legend of Ariadne, is the solving of a problem with multiple apparent means of proceeding - such as a physical maze, a logic puzzle, or an ethical dilemma - through an exhaustive application of logic to all available routes. It is the particular method used that is able to follow completely through to trace steps or take point by point a series of found truths in a contingent, ordered search that reaches a desired end position. This process can take the form of a mental record, a physical marking, or even a philosophical debate; it is the process itself that assumes the name.